Witnesses said the helicopter had burst into blames after hitting a house in the eastern Bagrami district of the Afghan capital. The house collapsed and rescuers were searching the rubble for more casualties.

Turkey confirmed one of its helicopters had crashed, but declined to give details of casualties.

The cause was being investigated and there were no reports of insurgent activity or fire in the area on Friday morning.

A statement from Nato headquarters in Kabul said: “Twelve [coalition] service members died following a helicopter crash in Kabul province today.

“The cause of the crash is under investigation, however initial reporting indicates there was no enemy activity in the area at the time of the crash.”

The 38-year-old father-of-two, from the Joint Base Lewis-McChord base in Washington, had been drinking with two other soldiers before wandering 500 yards from his base in Kandahar province, southern Afghanistan, and gunning down 16 villagers, the official said.

The soldier was suffering from stress over a fourth deployment and was under pressure from his wife, it was claimed. His lawyer John Henry Browne said he had been reluctant to return to the frontline.

He said soldiers in the suspect's camp had been very upset that somebody in their unit had their leg blown off the day before the rampage.

Mr Browne said his client is highly decorated, had twice been injured during tours in Iraq and was reluctant to leave on his fourth deployment. But he denied reports suggesting that the soldier had alcohol or marital problems.

Questions were raised earlier this week about the staff sergeant’s mental stability after it emerged that he was suffering from a head trauma from a roadside bomb in Iraq and another injury to his leg, where surgeons had to remove part of his foot.

His lawyer John Henry Browne would not confirm whether the staff sergeant had psychological or mental health issues but said claims he had marital issues were "hogwash" and "a bunch of nonsense".

"He's one of our boys and we need to treat him fairly," he added.

The soldier, who is originally from the Midwest, was deployed last December with the 3rd Stryker Brigade, and on Feb 1 was attached to a "village stability operation."

His lawyer described him as highly decorated and said he had once been nominated for a Bronze Star, which he did not receive.

The soldier was worried about being deployed a fourth time and didn't hold any animosity towards Muslims, his lawyer added.

"He wasn't thrilled about going on another deployment," said the lawyer, John Henry Browne. "He was told he wasn't going back, and then he was told he was going."

The suspect was "very quiet" when he spoke to him by phone and asked Mr Browne to send his love to his family, the lawyer said.

Mr Browne is known for representing Colton Harris-Moore, the so-called "Barefoot Bandit," who was found guilty of a string of audacious crimes across the United States and sentenced in January to six and a half years in prison. He was involved in the defence of Ted Bundy, the American serial killer.

The soldier, who has not been formally charged, was flown to an American detention site in Kuwait yesterday, to the fury of dozens of Afghans who have demanded he face trial in Afghanistan.

The Army has declined to name the staff sergeant further inflaming the issue.

Military officials are expected to transfer the staff sergeant to the United States later today after diplomatic outcry from the Kuwaitis, who were not told in advance that the soldier was being moved.

“When they learned about it, the Kuwaitis blew a gasket and wanted him out of there,” the official said.

The staff sergeant's wife and two children, aged three and four, were moved from their home to the Joint Base Lewis McChord in Washington in anticipation of the man's name being released.

If convicted, the soldier could face the death penalty under US military law.